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SUDOERS(5) MAINTENANCE COMMANDS SUDOERS(5) NAME sudoers - list of which users may execute what DESCRIPTION The sudoers file is composed of two types of entries: aliases (basi- cally variables) and user specifications (which specify who may run what). When multiple entries match for a user, they are applied in order. Where there are multiple matches, the last match is used (which is not necessarily the most specific match). The sudoers grammar will be described below in Extended Backus-Naur Form (EBNF). Don't despair if you don't know what EBNF is; it is fairly simple, and the definitions below are annotated. Quick guide to EBNF EBNF is a concise and exact way of describing the grammar of a lan- guage. Each EBNF definition is made up of production rules. E.g., symbol ::= definition | alternate1 | alternate2 ... Each production rule references others and thus makes up a grammar for the language. EBNF also contains the following operators, which many readers will recognize from regular expressions. Do not, however, con- fuse them with "wildcard" characters, which have different meanings. ? Means that the preceding symbol (or group of symbols) is optional. That is, it may appear once or not at all. * Means that the preceding symbol (or group of symbols) may appear zero or more times. + Means that the preceding symbol (or group of symbols) may appear one or more times. Parentheses may be used to group symbols together. For clarity, we will use single quotes ('') to designate what is a verbatim character string (as opposed to a symbol name). Aliases There are four kinds of aliases: User_Alias, Runas_Alias, Host_Alias and Cmnd_Alias. Alias ::= 'User_Alias' User_Alias (':' User_Alias)* | 'Runas_Alias' Runas_Alias (':' Runas_Alias)* | 'Host_Alias' Host_Alias (':' Host_Alias)* | 'Cmnd_Alias' Cmnd_Alias (':' Cmnd_Alias)* User_Alias ::= NAME '=' User_List Runas_Alias ::= NAME '=' Runas_List Host_Alias ::= NAME '=' Host_List Cmnd_Alias ::= NAME '=' Cmnd_List NAME ::= [A-Z]([A-Z][0-9]_)* Each alias definition is of the form Alias_Type NAME = item1, item2, ... where Alias_Type is one of User_Alias, Runas_Alias, Host_Alias, or Cmnd_Alias. A NAME is a string of uppercase letters, numbers, and un- derscore characters ('_'). A NAME must start with an uppercase letter. It is possible to put several alias definitions of the same type on a single line, joined by a colon (':'). E.g., Alias_Type NAME = item1, item2, item3 : NAME = item4, item5 The definitions of what constitutes a valid alias member follow. User_List ::= User | User ',' User_List User ::= '!'* username | '!'* '%'group | '!'* '+'netgroup | '!'* User_Alias A User_List is made up of one or more usernames, system groups (pre- fixed with '%'), netgroups (prefixed with '+') and other aliases. Each list item may be prefixed with one or more '!' operators. An odd num- ber of '!' operators negate the value of the item; an even number just cancel each other out. Runas_List ::= Runas_User | Runas_User ',' Runas_List Runas_User ::= '!'* username | '!'* '#'uid | '!'* '%'group | '!'* +netgroup | '!'* Runas_Alias A Runas_List is similar to a User_List except that it can also contain uids (prefixed with '#') and instead of User_Aliases it can contain Runas_Aliases. Note that usernames and groups are matched as strings. In other words, two users (groups) with the same uid (gid) are consid- ered to be distinct. If you wish to match all usernames with the same uid (e.g. root and toor), you can use a uid instead (#0 in the example given). Host_List ::= Host | Host ',' Host_List Host ::= '!'* hostname | '!'* ip_addr | '!'* network(/netmask)? | '!'* '+'netgroup | '!'* Host_Alias A Host_List is made up of one or more hostnames, IP addresses, network numbers, netgroups (prefixed with '+') and other aliases. Again, the value of an item may be negated with the '!' operator. If you do not specify a netmask along with the network number, sudo will query each of the local host's network interfaces and, if the network number cor- responds to one of the hosts's network interfaces, the corresponding netmask will be used. The netmask may be specified either in standard IP address notation (e.g. 255.255.255.0 or ffff:ffff:ffff:ffff::), or CIDR notation (number of bits, e.g. 24 or 64). A hostname may include shell-style wildcards (see the Wildcards section below), but unless the hostname command on your machine returns the fully qualified hostname, you'll need to use the fqdn option for wildcards to be useful. Cmnd_List ::= Cmnd | Cmnd ',' Cmnd_List commandname ::= filename | filename args | filename '""' Cmnd ::= '!'* commandname | '!'* directory | '!'* "sudoedit" | '!'* Cmnd_Alias A Cmnd_List is a list of one or more commandnames, directories, and other aliases. A commandname is a fully qualified filename which may include shell-style wildcards (see the Wildcards section below). A simple filename allows the user to run the command with any arguments he/she wishes. However, you may also specify command line arguments (including wildcards). Alternately, you can specify "" to indicate that the command may only be run without command line arguments. A di- rectory is a fully qualified pathname ending in a '/'. When you spec- ify a directory in a Cmnd_List, the user will be able to run any file within that directory (but not in any subdirectories therein). If a Cmnd has associated command line arguments, then the arguments in the Cmnd must match exactly those given by the user on the command line (or match the wildcards if there are any). Note that the following characters must be escaped with a '\' if they are used in command argu- ments: ',', ':', '=', '\'. The special command "sudoedit" is used to permit a user to run sudo with the -e flag (or as sudoedit). It may take command line arguments just as a normal command does. Defaults Certain configuration options may be changed from their default values at runtime via one or more Default_Entry lines. These may affect all users on any host, all users on a specific host, a specific user, or commands being run as a specific user. Default_Type ::= 'Defaults' | 'Defaults' '@' Host_List | 'Defaults' ':' User_List | 'Defaults' '>' Runas_List Default_Entry ::= Default_Type Parameter_List Parameter_List ::= Parameter | Parameter ',' Parameter_List Parameter ::= Parameter '=' Value | Parameter '+=' Value | Parameter '-=' Value | '!'* Parameter Parameters may be flags, integer values, strings, or lists. Flags are implicitly boolean and can be turned off via the '!' operator. Some integer, string and list parameters may also be used in a boolean con- text to disable them. Values may be enclosed in double quotes (") when they contain multiple words. Special characters may be escaped with a backslash (\). Lists have two additional assignment operators, += and -=. These oper- ators are used to add to and delete from a list respectively. It is not an error to use the -= operator to remove an element that does not exist in a list. See "SUDOERS OPTIONS" for a list of supported Defaults parameters. User Specification User_Spec ::= User_List Host_List '=' Cmnd_Spec_List \ (':' Host_List '=' Cmnd_Spec_List)* Cmnd_Spec_List ::= Cmnd_Spec | Cmnd_Spec ',' Cmnd_Spec_List Cmnd_Spec ::= Runas_Spec? Tag_Spec* Cmnd Runas_Spec ::= '(' Runas_List ')' Tag_Spec ::= ('NOPASSWD:' | 'PASSWD:' | 'NOEXEC:' | 'EXEC:' | 'SETENV:' | 'NOSETENV:') A user specification determines which commands a user may run (and as what user) on specified hosts. By default, commands are run as root, but this can be changed on a per-command basis. Let's break that down into its constituent parts: Runas_Spec A Runas_Spec is simply a Runas_List (as defined above) enclosed in a set of parentheses. If you do not specify a Runas_Spec in the user specification, a default Runas_Spec of root will be used. A Runas_Spec sets the default for commands that follow it. What this means is that for the entry: dgb boulder = (operator) /bin/ls, /bin/kill, /usr/bin/lprm The user dgb may run /bin/ls, /bin/kill, and /usr/bin/lprm -- but only as operator. E.g., $ sudo -u operator /bin/ls. It is also possible to override a Runas_Spec later on in an entry. If we modify the entry like so: dgb boulder = (operator) /bin/ls, (root) /bin/kill, /usr/bin/lprm Then user dgb is now allowed to run /bin/ls as operator, but /bin/kill and /usr/bin/lprm as root. Tag_Spec A command may have zero or more tags associated with it. There are six possible tag values, NOPASSWD, PASSWD, NOEXEC, EXEC, SETENV and NOSETENV. Once a tag is set on a Cmnd, subsequent Cmnds in the Cmnd_Spec_List, inherit the tag unless it is overridden by the opposite tag (i.e.: PASSWD overrides NOPASSWD and NOEXEC overrides EXEC). NOPASSWD and PASSWD By default, sudo requires that a user authenticate him or herself be- fore running a command. This behavior can be modified via the NOPASSWD tag. Like a Runas_Spec, the NOPASSWD tag sets a default for the com- mands that follow it in the Cmnd_Spec_List. Conversely, the PASSWD tag can be used to reverse things. For example: ray rushmore = NOPASSWD: /bin/kill, /bin/ls, /usr/bin/lprm would allow the user ray to run /bin/kill, /bin/ls, and /usr/bin/lprm as root on the machine rushmore as root without authenticating himself. If we only want ray to be able to run /bin/kill without a password the entry would be: ray rushmore = NOPASSWD: /bin/kill, PASSWD: /bin/ls, /usr/bin/lprm Note, however, that the PASSWD tag has no effect on users who are in the group specified by the exempt_group option. By default, if the NOPASSWD tag is applied to any of the entries for a user on the current host, he or she will be able to run sudo -l without a password. Additionally, a user may only run sudo -v without a pass- word if the NOPASSWD tag is present for all a user's entries that per- tain to the current host. This behavior may be overridden via the ver- ifypw and listpw options. NOEXEC and EXEC If sudo has been compiled with noexec support and the underlying oper- ating system supports it, the NOEXEC tag can be used to prevent a dy- namically-linked executable from running further commands itself. In the following example, user aaron may run /usr/bin/more and /usr/bin/vi but shell escapes will be disabled. aaron shanty = NOEXEC: /usr/bin/more, /usr/bin/vi See the "PREVENTING SHELL ESCAPES" section below for more details on how NOEXEC works and whether or not it will work on your system. SETENV and NOSETENV These tags override the value of the setenv option on a per-command ba- sis. Note that if SETENV has been set for a command, any environment variables set on the command line way are not subject to the restric- tions imposed by env_check, env_delete, or env_keep. As such, only trusted users should be allowed to set variables in this manner. If the command matched is ALL, the SETENV tag is implied for that command; this default may be overridden by use of the UNSETENV tag. Wildcards sudo allows shell-style wildcards (aka meta or glob characters) to be used in pathnames as well as command line arguments in the sudoers file. Wildcard matching is done via the POSIX fnmatch(3) routine. Note that these are not regular expressions. * Matches any set of zero or more characters. ? Matches any single character. [...] Matches any character in the specified range. [!...] Matches any character not in the specified range. \x For any character "x", evaluates to "x". This is used to es- cape special characters such as: "*", "?", "[", and "}". Note that a forward slash ('/') will not be matched by wildcards used in the pathname. When matching the command line arguments, however, a slash does get matched by wildcards. This is to make a path like: /usr/bin/* match /usr/bin/who but not /usr/bin/X11/xterm. Exceptions to wildcard rules The following exceptions apply to the above rules: "" If the empty string "" is the only command line argument in the sudoers entry it means that command is not allowed to be run with any arguments. Other special characters and reserved words The pound sign ('#') is used to indicate a comment (unless it is part of a #include directive or unless it occurs in the context of a user name and is followed by one or more digits, in which case it is treated as a uid). Both the comment character and any text after it, up to the end of the line, are ignored. The reserved word ALL is a built-in alias that always causes a match to succeed. It can be used wherever one might otherwise use a Cmnd_Alias, User_Alias, Runas_Alias, or Host_Alias. You should not try to define your own alias called ALL as the built-in alias will be used in prefer- ence to your own. Please note that using ALL can be dangerous since in a command context, it allows the user to run any command on the system. An exclamation point ('!') can be used as a logical not operator both in an alias and in front of a Cmnd. This allows one to exclude certain values. Note, however, that using a ! in conjunction with the built-in ALL alias to allow a user to run "all but a few" commands rarely works as intended (see SECURITY NOTES below). Long lines can be continued with a backslash ('\') as the last charac- ter on the line. Whitespace between elements in a list as well as special syntactic characters in a User Specification ('=', ':', '(', ')') is optional. The following characters must be escaped with a backslash ('\') when used as part of a word (e.g. a username or hostname): '@', '!', '=', ':', ',', '(', ')', '\'. SUDOERS OPTIONS sudo's behavior can be modified by Default_Entry lines, as explained earlier. A list of all supported Defaults parameters, grouped by type, are listed below. Flags: always_set_home If set, sudo will set the HOME environment variable to the home directory of the target user (which is root unless the -u option is used). This effectively means that the -H flag is always implied. This flag is off by default. authenticate If set, users must authenticate themselves via a pass- word (or other means of authentication) before they may run commands. This default may be overridden via the PASSWD and NOPASSWD tags. This flag is on by default. env_editor If set, visudo will use the value of the EDITOR or VI- SUAL environment variables before falling back on the default editor list. Note that this may create a secu- rity hole as it allows the user to run any arbitrary command as root without logging. A safer alternative is to place a colon-separated list of editors in the editor variable. visudo will then only use the EDITOR or VISUAL if they match a value specified in editor. This flag is on by default. env_reset If set, sudo will reset the environment to only contain the LOGNAME, SHELL, USER, USERNAME and the SUDO_* vari- ables. Any variables in the caller's environment that match the env_keep and env_check lists are then added. The default contents of the env_keep and env_check lists are displayed when sudo is run by root with the -V option. If sudo was compiled with the SECURE_PATH option, its value will be used for the PATH environment variable. This flag is on by default. fqdn Set this flag if you want to put fully qualified host- names in the sudoers file. I.e., instead of myhost you would use myhost.mydomain.edu. You may still use the short form if you wish (and even mix the two). Beware that turning on fqdn requires sudo to make DNS lookups which may make sudo unusable if DNS stops working (for example if the machine is not plugged into the net- work). Also note that you must use the host's official name as DNS knows it. That is, you may not use a host alias (CNAME entry) due to performance issues and the fact that there is no way to get all aliases from DNS. If your machine's hostname (as returned by the hostname command) is already fully qualified you shouldn't need to set fqdn. This flag is off by default. ignore_dot If set, sudo will ignore '.' or '' (current dir) in the PATH environment variable; the PATH itself is not modi- fied. This flag is on by default. Currently, while it is possible to set ignore_dot in sudoers, its value is not used. This option should be considered read-only (it will be fixed in a future version of sudo). ignore_local_sudoers If set via LDAP, parsing of /usr/local/etc/sudoers will be skipped. This is intended for Enterprises that wish to prevent the usage of local sudoers files so that only LDAP is used. This thwarts the efforts of rogue operators who would attempt to add roles to /usr/lo- cal/etc/sudoers. When this option is present, /usr/lo- cal/etc/sudoers does not even need to exist. Since this option tells sudo how to behave when no specific LDAP entries have been matched, this sudoOption is only meaningful for the cn=defaults section. This flag is off by default. insults If set, sudo will insult users when they enter an in- correct password. This flag is off by default. log_host If set, the hostname will be logged in the (non-syslog) sudo log file. This flag is off by default. log_year If set, the four-digit year will be logged in the (non-syslog) sudo log file. This flag is off by de- fault. long_otp_prompt When validating with a One Time Password (OPT) scheme such as S/Key or OPIE, a two-line prompt is used to make it easier to cut and paste the challenge to a lo- cal window. It's not as pretty as the default but some people find it more convenient. This flag is on by de- fault. mail_always Send mail to the mailto user every time a users runs sudo. This flag is off by default. mail_badpass Send mail to the mailto user if the user running sudo does not enter the correct password. This flag is off by default. mail_no_host If set, mail will be sent to the mailto user if the in- voking user exists in the sudoers file, but is not al- lowed to run commands on the current host. This flag is off by default. mail_no_perms If set, mail will be sent to the mailto user if the in- voking user is allowed to use sudo but the command they are trying is not listed in their sudoers file entry or is explicitly denied. This flag is off by default. mail_no_user If set, mail will be sent to the mailto user if the in- voking user is not in the sudoers file. This flag is on by default. noexec If set, all commands run via sudo will behave as if the NOEXEC tag has been set, unless overridden by a EXEC tag. See the description of NOEXEC and EXEC below as well as the "PREVENTING SHELL ESCAPES" section at the end of this manual. This flag is off by default. path_info Normally, sudo will tell the user when a command could not be found in their PATH environment variable. Some sites may wish to disable this as it could be used to gather information on the location of executables that the normal user does not have access to. The disadvan- tage is that if the executable is simply not in the user's PATH, sudo will tell the user that they are not allowed to run it, which can be confusing. This flag is on by default. passprompt_override The password prompt specified by passprompt will nor- mally only be used if the passwod prompt provided by systems such as PAM matches the string "Password:". If passprompt_override is set, passprompt will always be used. This flag is off by default. preserve_groups By default sudo will initialize the group vector to the list of groups the target user is in. When pre- serve_groups is set, the user's existing group vector is left unaltered. The real and effective group IDs, however, are still set to match the target user. This flag is off by default. requiretty If set, sudo will only run when the user is logged in to a real tty. This will disallow things like "rsh somehost sudo ls" since rsh(1) does not allocate a tty. Because it is not possible to turn off echo when there is no tty present, some sites may wish to set this flag to prevent a user from entering a visible password. This flag is off by default. root_sudo If set, root is allowed to run sudo too. Disabling this prevents users from "chaining" sudo commands to get a root shell by doing something like "sudo sudo /bin/sh". Note, however, that turning off root_sudo will also prevent root and from running sudoedit. Dis- abling root_sudo provides no real additional security; it exists purely for historical reasons. This flag is on by default. rootpw If set, sudo will prompt for the root password instead of the password of the invoking user. This flag is off by default. runaspw If set, sudo will prompt for the password of the user defined by the runas_default option (defaults to root) instead of the password of the invoking user. This flag is off by default. set_home If set and sudo is invoked with the -s flag the HOME environment variable will be set to the home directory of the target user (which is root unless the -u option is used). This effectively makes the -s flag imply -H. This flag is off by default. set_logname Normally, sudo will set the LOGNAME, USER and USERNAME environment variables to the name of the target user (usually root unless the -u flag is given). However, since some programs (including the RCS revision control system) use LOGNAME to determine the real identity of the user, it may be desirable to change this behavior. This can be done by negating the set_logname option. Note that if the env_reset option has not been dis- abled, entries in the env_keep list will override the value of set_logname. This flag is off by default. setenv Allow the user to disable the env_reset option from the command line. Additionally, environment variables set via the command line are not subject to the restric- tions imposed by env_check, env_delete, or env_keep. As such, only trusted users should be allowed to set variables in this manner. This flag is off by default. shell_noargs If set and sudo is invoked with no arguments it acts as if the -s flag had been given. That is, it runs a shell as root (the shell is determined by the SHELL en- vironment variable if it is set, falling back on the shell listed in the invoking user's /etc/passwd entry if not). This flag is off by default. stay_setuid Normally, when sudo executes a command the real and ef- fective UIDs are set to the target user (root by de- fault). This option changes that behavior such that the real UID is left as the invoking user's UID. In other words, this makes sudo act as a setuid wrapper. This can be useful on systems that disable some poten- tially dangerous functionality when a program is run setuid. This option is only effective on systems with either the setreuid() or setresuid() function. This flag is off by default. targetpw If set, sudo will prompt for the password of the user specified by the -u flag (defaults to root) instead of the password of the invoking user. Note that this pre- cludes the use of a uid not listed in the passwd data- base as an argument to the -u flag. This flag is off by default. tty_tickets If set, users must authenticate on a per-tty basis. Normally, sudo uses a directory in the ticket dir with the same name as the user running it. With this flag enabled, sudo will use a file named for the tty the user is logged in on in that directory. This flag is on by default. use_loginclass If set, sudo will apply the defaults specified for the target user's login class if one exists. Only avail- able if sudo is configured with the --with-logincap op- tion. This flag is off by default. Integers: passwd_tries The number of tries a user gets to enter his/her pass- word before sudo logs the failure and exits. The de- fault is 3. Integers that can be used in a boolean context: loglinelen Number of characters per line for the file log. This value is used to decide when to wrap lines for nicer log files. This has no effect on the syslog log file, only the file log. The default is 80 (use 0 or negate the option to disable word wrap). passwd_timeout Number of minutes before the sudo password prompt times out. The default is 5; set this to 0 for no password timeout. timestamp_timeout Number of minutes that can elapse before sudo will ask for a passwd again. The default is 5. Set this to 0 to always prompt for a password. If set to a value less than 0 the user's timestamp will never expire. This can be used to allow users to create or delete their own timestamps via sudo -v and sudo -k respec- tively. umask Umask to use when running the command. Negate this op- tion or set it to 0777 to preserve the user's umask. The default is 0022. Strings: badpass_message Message that is displayed if a user enters an incorrect password. The default is Sorry, try again. unless in- sults are enabled. editor A colon (':') separated list of editors allowed to be used with visudo. visudo will choose the editor that matches the user's EDITOR environment variable if pos- sible, or the first editor in the list that exists and is executable. The default is the path to vi on your system. mailsub Subject of the mail sent to the mailto user. The escape %h will expand to the hostname of the machine. Default is *** SECURITY information for %h ***. noexec_file Path to a shared library containing dummy versions of the execv(), execve() and fexecve() library functions that just return an error. This is used to implement the noexec functionality on systems that support LD_PRELOAD or its equivalent. Defaults to /usr/lo- cal/libexec/sudo_noexec.so. passprompt The default prompt to use when asking for a password; can be overridden via the -p option or the SUDO_PROMPT environment variable. The following percent (`%') es- capes are supported: %H expanded to the local hostname including the domain name (on if the machine's hostname is fully quali- fied or the fqdn option is set) %h expanded to the local hostname without the domain name %p expanded to the user whose password is being asked for (respects the rootpw, targetpw and runaspw flags in sudoers) %U expanded to the login name of the user the command will be run as (defaults to root) %u expanded to the invoking user's login name %% two consecutive % characters are collapsed into a single % character The default value is Password:. runas_default The default user to run commands as if the -u flag is not specified on the command line. This defaults to root. Note that if runas_default is set it must occur before any Runas_Alias specifications. syslog_badpri Syslog priority to use when user authenticates unsuc- cessfully. Defaults to alert. syslog_goodpri Syslog priority to use when user authenticates success- fully. Defaults to notice. timestampdir The directory in which sudo stores its timestamp files. The default is /var/run/sudo. timestampowner The owner of the timestamp directory and the timestamps stored therein. The default is root. Strings that can be used in a boolean context: exempt_group Users in this group are exempt from password and PATH re- quirements. This is not set by default. lecture This option controls when a short lecture will be printed along with the password prompt. It has the following pos- sible values: always Always lecture the user. never Never lecture the user. once Only lecture the user the first time they run sudo. If no value is specified, a value of once is implied. Negating the option results in a value of never being used. The default value is once. lecture_file Path to a file containing an alternate sudo lecture that will be used in place of the standard lecture if the named file exists. By default, sudo uses a built-in lecture. listpw This option controls when a password will be required when a user runs sudo with the -l flag. It has the following possible values: all All the user's sudoers entries for the current host must have the NOPASSWD flag set to avoid entering a password. always The user must always enter a password to use the -l flag. any At least one of the user's sudoers entries for the current host must have the NOPASSWD flag set to avoid entering a password. never The user need never enter a password to use the -l flag. If no value is specified, a value of any is implied. Negating the option results in a value of never being used. The default value is any. logfile Path to the sudo log file (not the syslog log file). Set- ting a path turns on logging to a file; negating this op- tion turns it off. By default, sudo logs via syslog. mailerflags Flags to use when invoking mailer. Defaults to -t. mailerpath Path to mail program used to send warning mail. Defaults to the path to sendmail found at configure time. mailto Address to send warning and error mail to. The address should be enclosed in double quotes (") to protect against sudo interpreting the @ sign. Defaults to root. syslog Syslog facility if syslog is being used for logging (negate to disable syslog logging). Defaults to local2. verifypw This option controls when a password will be required when a user runs sudo with the -v flag. It has the following possible values: all All the user's sudoers entries for the current host must have the NOPASSWD flag set to avoid entering a password. always The user must always enter a password to use the -v flag. any At least one of the user's sudoers entries for the current host must have the NOPASSWD flag set to avoid entering a password. never The user need never enter a password to use the -v flag. If no value is specified, a value of all is implied. Negating the option results in a value of never being used. The default value is all. Lists that can be used in a boolean context: env_check Environment variables to be removed from the user's en- vironment if the variable's value contains % or / char- acters. This can be used to guard against printf-style format vulnerabilities in poorly-written programs. The argument may be a double-quoted, space-separated list or a single value without double-quotes. The list can be replaced, added to, deleted from, or disabled by us- ing the =, +=, -=, and ! operators respectively. Re- gardless of whether the env_reset option is enabled or disabled, variables specified by env_check will be pre- served in the environment if they pass the aforemen- tioned check. The default list of environment vari- ables to check is displayed when sudo is run by root with the -V option. env_delete Environment variables to be removed from the user's en- vironment. The argument may be a double-quoted, space- separated list or a single value without double-quotes. The list can be replaced, added to, deleted from, or disabled by using the =, +=, -=, and ! operators re- spectively. The default list of environment variables to remove is displayed when sudo is run by root with the -V option. Note that many operating systems will remove potentially dangerous variables from the envi- ronment of any setuid process (such as sudo). env_keep Environment variables to be preserved in the user's en- vironment when the env_reset option is in effect. This allows fine-grained control over the environment sudo-spawned processes will receive. The argument may be a double-quoted, space-separated list or a single value without double-quotes. The list can be replaced, added to, deleted from, or disabled by using the =, +=, -=, and ! operators respectively. The default list of variables to keep is displayed when sudo is run by root with the -V option. When logging via syslog(3), sudo accepts the following values for the syslog facility (the value of the syslog Parameter): authpriv (if your OS supports it), auth, daemon, user, local0, local1, local2, local3, local4, local5, local6, and local7. The following syslog priorities are supported: alert, crit, debug, emerg, err, info, notice, and warn- ing. FILES /usr/local/etc/sudoers List of who can run what /etc/group Local groups file /etc/netgroup List of network groups EXAMPLES Since the sudoers file is parsed in a single pass, order is important. In general, you should structure sudoers such that the Host_Alias, User_Alias, and Cmnd_Alias specifications come first, followed by any Default_Entry lines, and finally the Runas_Alias and user specifica- tions. The basic rule of thumb is you cannot reference an Alias that has not already been defined. Below are example sudoers entries. Admittedly, some of these are a bit contrived. First, we define our aliases: # User alias specification User_Alias FULLTIMERS = millert, mikef, dowdy User_Alias PARTTIMERS = bostley, jwfox, crawl User_Alias WEBMASTERS = will, wendy, wim # Runas alias specification Runas_Alias OP = root, operator Runas_Alias DB = oracle, sybase # Host alias specification Host_Alias SPARC = bigtime, eclipse, moet, anchor :\ SGI = grolsch, dandelion, black :\ ALPHA = widget, thalamus, foobar :\ HPPA = boa, nag, python Host_Alias CUNETS = 128.138.0.0/255.255.0.0 Host_Alias CSNETS = 128.138.243.0, 128.138.204.0/24, 128.138.242.0 Host_Alias SERVERS = master, mail, www, ns Host_Alias CDROM = orion, perseus, hercules # Cmnd alias specification Cmnd_Alias DUMPS = /usr/bin/mt, /usr/sbin/dump, /usr/sbin/rdump,\ /usr/sbin/restore, /usr/sbin/rrestore Cmnd_Alias KILL = /usr/bin/kill Cmnd_Alias PRINTING = /usr/sbin/lpc, /usr/bin/lprm Cmnd_Alias SHUTDOWN = /usr/sbin/shutdown Cmnd_Alias HALT = /usr/sbin/halt Cmnd_Alias REBOOT = /usr/sbin/reboot Cmnd_Alias SHELLS = /usr/bin/sh, /usr/bin/csh, /usr/bin/ksh, \ /usr/local/bin/tcsh, /usr/bin/rsh, \ /usr/local/bin/zsh Cmnd_Alias SU = /usr/bin/su Cmnd_Alias PAGERS = /usr/bin/more, /usr/bin/pg, /usr/bin/less Here we override some of the compiled in default values. We want sudo to log via syslog(3) using the auth facility in all cases. We don't want to subject the full time staff to the sudo lecture, user millert need not give a password, and we don't want to reset the LOGNAME, USER or USERNAME environment variables when running commands as root. Addi- tionally, on the machines in the SERVERS Host_Alias, we keep an addi- tional local log file and make sure we log the year in each log line since the log entries will be kept around for several years. Lastly, we disable shell escapes for the commands in the PAGERS Cmnd_Alias (/usr/bin/more, /usr/bin/pg and /usr/bin/less). # Override built-in defaults Defaults syslog=auth Defaults>root !set_logname Defaults:FULLTIMERS !lecture Defaults:millert !authenticate Defaults@SERVERS log_year, logfile=/var/log/sudo.log Defaults!PAGERS noexec The User specification is the part that actually determines who may run what. root ALL = (ALL) ALL %wheel ALL = (ALL) ALL We let root and any user in group wheel run any command on any host as any user. FULLTIMERS ALL = NOPASSWD: ALL Full time sysadmins (millert, mikef, and dowdy) may run any command on any host without authenticating themselves. PARTTIMERS ALL = ALL Part time sysadmins (bostley, jwfox, and crawl) may run any command on any host but they must authenticate themselves first (since the entry lacks the NOPASSWD tag). jack CSNETS = ALL The user jack may run any command on the machines in the CSNETS alias (the networks 128.138.243.0, 128.138.204.0, and 128.138.242.0). Of those networks, only 128.138.204.0 has an explicit netmask (in CIDR no- tation) indicating it is a class C network. For the other networks in CSNETS, the local machine's netmask will be used during matching. lisa CUNETS = ALL The user lisa may run any command on any host in the CUNETS alias (the class B network 128.138.0.0). operator ALL = DUMPS, KILL, SHUTDOWN, HALT, REBOOT, PRINTING,\ sudoedit /etc/printcap, /usr/oper/bin/ The operator user may run commands limited to simple maintenance. Here, those are commands related to backups, killing processes, the printing system, shutting down the system, and any commands in the di- rectory /usr/oper/bin/. joe ALL = /usr/bin/su operator The user joe may only su(1) to operator. pete HPPA = /usr/bin/passwd [A-z]*, !/usr/bin/passwd root The user pete is allowed to change anyone's password except for root on the HPPA machines. Note that this assumes passwd(1) does not take mul- tiple usernames on the command line. bob SPARC = (OP) ALL : SGI = (OP) ALL The user bob may run anything on the SPARC and SGI machines as any user listed in the OP Runas_Alias (root and operator). jim +biglab = ALL The user jim may run any command on machines in the biglab netgroup. sudo knows that "biglab" is a netgroup due to the '+' prefix. +secretaries ALL = PRINTING, /usr/bin/adduser, /usr/bin/rmuser Users in the secretaries netgroup need to help manage the printers as well as add and remove users, so they are allowed to run those commands on all machines. fred ALL = (DB) NOPASSWD: ALL The user fred can run commands as any user in the DB Runas_Alias (ora- cle or sybase) without giving a password. john ALPHA = /usr/bin/su [!-]*, !/usr/bin/su *root* On the ALPHA machines, user john may su to anyone except root but he is not allowed to give su(1) any flags. jen ALL, !SERVERS = ALL The user jen may run any command on any machine except for those in the SERVERS Host_Alias (master, mail, www and ns). jill SERVERS = /usr/bin/, !SU, !SHELLS For any machine in the SERVERS Host_Alias, jill may run any commands in the directory /usr/bin/ except for those commands belonging to the SU and SHELLS Cmnd_Aliases. steve CSNETS = (operator) /usr/local/op_commands/ The user steve may run any command in the directory /usr/local/op_com- mands/ but only as user operator. matt valkyrie = KILL On his personal workstation, valkyrie, matt needs to be able to kill hung processes. WEBMASTERS www = (www) ALL, (root) /usr/bin/su www On the host www, any user in the WEBMASTERS User_Alias (will, wendy, and wim), may run any command as user www (which owns the web pages) or simply su(1) to www. ALL CDROM = NOPASSWD: /sbin/umount /CDROM,\ /sbin/mount -o nosuid\,nodev /dev/cd0a /CDROM Any user may mount or unmount a CD-ROM on the machines in the CDROM Host_Alias (orion, perseus, hercules) without entering a password. This is a bit tedious for users to type, so it is a prime candidate for encapsulating in a shell script. SECURITY NOTES It is generally not effective to "subtract" commands from ALL using the '!' operator. A user can trivially circumvent this by copying the de- sired command to a different name and then executing that. For exam- ple: bill ALL = ALL, !SU, !SHELLS Doesn't really prevent bill from running the commands listed in SU or SHELLS since he can simply copy those commands to a different name, or use a shell escape from an editor or other program. Therefore, these kind of restrictions should be considered advisory at best (and rein- forced by policy). PREVENTING SHELL ESCAPES Once sudo executes a program, that program is free to do whatever it pleases, including run other programs. This can be a security issue since it is not uncommon for a program to allow shell escapes, which lets a user bypass sudo's access control and logging. Common programs that permit shell escapes include shells (obviously), editors, pagina- tors, mail and terminal programs. There are two basic approaches to this problem: restrict Avoid giving users access to commands that allow the user to run arbitrary commands. Many editors have a restricted mode where shell escapes are disabled, though sudoedit is a better solution to running editors via sudo. Due to the large num- ber of programs that offer shell escapes, restricting users to the set of programs that do not if often unworkable. noexec Many systems that support shared libraries have the ability to override default library functions by pointing an environ- ment variable (usually LD_PRELOAD) to an alternate shared li- brary. On such systems, sudo's noexec functionality can be used to prevent a program run by sudo from executing any other programs. Note, however, that this applies only to na- tive dynamically-linked executables. Statically-linked exe- cutables and foreign executables running under binary emula- tion are not affected. To tell whether or not sudo supports noexec, you can run the following as root: sudo -V | grep "dummy exec" If the resulting output contains a line that begins with: File containing dummy exec functions: then sudo may be able to replace the exec family of functions in the standard library with its own that simply return an error. Unfortunately, there is no foolproof way to know whether or not noexec will work at compile-time. noexec should work on SunOS, Solaris, *BSD, Linux, IRIX, Tru64 UNIX, MacOS X, and HP-UX 11.x. It is known not to work on AIX and UnixWare. noexec is expected to work on most operating sys- tems that support the LD_PRELOAD environment variable. Check your operating system's manual pages for the dynamic linker (usually ld.so, ld.so.1, dyld, dld.sl, rld, or loader) to see if LD_PRELOAD is supported. To enable noexec for a command, use the NOEXEC tag as docu- mented in the User Specification section above. Here is that example again: aaron shanty = NOEXEC: /usr/bin/more, /usr/bin/vi This allows user aaron to run /usr/bin/more and /usr/bin/vi with noexec enabled. This will prevent those two commands from executing other commands (such as a shell). If you are unsure whether or not your system is capable of supporting noexec you can always just try it out and see if it works. Note that restricting shell escapes is not a panacea. Programs running as root are still capable of many potentially hazardous operations (such as changing or overwriting files) that could lead to unintended privilege escalation. In the specific case of an editor, a safer ap- proach is to give the user permission to run sudoedit. SEE ALSO rsh(1), su(1), fnmatch(3), sudo(8), visudo(8) CAVEATS The sudoers file should always be edited by the visudo command which locks the file and does grammatical checking. It is imperative that su- doers be free of syntax errors since sudo will not run with a syntacti- cally incorrect sudoers file. When using netgroups of machines (as opposed to users), if you store fully qualified hostnames in the netgroup (as is usually the case), you either need to have the machine's hostname be fully qualified as re- turned by the hostname command or use the fqdn option in sudoers. BUGS If you feel you have found a bug in sudo, please submit a bug report at http://www.sudo.ws/sudo/bugs/ SUPPORT Limited free support is available via the sudo-users mailing list, see http://www.sudo.ws/mailman/listinfo/sudo-users to subscribe or search the archives. DISCLAIMER sudo is provided ``AS IS'' and any express or implied warranties, in- cluding, but not limited to, the implied warranties of merchantability and fitness for a particular purpose are disclaimed. See the LICENSE file distributed with sudo or http://www.sudo.ws/sudo/license.html for complete details. 1.6.9p17 Jun 21, 2008 SUDOERS(5)
NAME | DESCRIPTION | SUDOERS OPTIONS | FILES | EXAMPLES | SECURITY NOTES | PREVENTING SHELL ESCAPES | SEE ALSO | CAVEATS | BUGS | SUPPORT | DISCLAIMER
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